It is often desirable or necessary to monitor objects, people, animals or places, which may involve the monitoring of information about the objects, people, animals or places; locating the objects, people, animals or places; and/or tracking the objects, people, animals, or places. One approach for monitoring, for example, an object involves associating an active tag with the object. An active tag transmits an radio frequency (RF) signal that can be received by a suitable receiver, which can demodulate the signal to determine the tag's identification and be used to locate the tag. Active tags can be transmit-only devices or can be transceivers capable of transmitting and receiving. Transmit-only tags can transmit continuously or periodically (e.g., for 1 second every 10 seconds). Such tags may stay in a powered down ‘sleep’ mode until interrogated in which case they ‘power up’ and begin transmitting. Transmit-only tags can be associated with a sensor or some other device and transmit only when a condition is met (e.g., smoke is detected). Transceiver-type tags may continuously or periodically (e.g., for 1 second every 10 seconds) ‘listen’ for a ‘tag request’ signal, which can be received and demodulated, and if the received signal has the appropriate data (e.g., the identifier for a particular tag or tags), then one or more of the tags may respond.
Another approach for monitoring an object, for example, involves associating an inductive RFID tag with the object. With this approach an interrogator uses a loop of wire to inductively communicate with and possibly power the inductive tag by modulating the loading of the loop with a modulation signal.
A passive approach for monitoring an object, for example, involves associating a RF backscatter tag with the object. An RF backscatter tag consists of a resonant antenna having a resistive load placed across its terminals that is varied to impose an Amplitude Modulated (AM) envelope onto its reflection characteristics, thereby conveying a signal back to an interrogator via the modulated reflection. The receive antenna is usually connected to a rectifier that converts the RF received from the interrogator to DC to power the circuit. These passive tags typically operate in the microwave spectrum. Existing passive tags, however, have limited signal-to-noise (SNR) and thus require the interrogator to be within close range of the tag and/or operate at a low data rate. As such, a system and method is needed that significantly increases the signal-to-noise (SNR) of passive tags in order to allow tracking and locating at much greater ranges and much higher data rates.